This invention relates generally to magnetic sensors and, more particularly, but not exclusively, to magnetic torque sensors employed in power steering systems in vehicles.
Such systems traditionally include a torque sensor mounted in relation to the vehicle""s steering device. Already known in the prior art are torque sensors that use the Hall-effect, for example, as described in document FR-A-2 689 633. There are also known torque sensors that detect the relative movement between, on the one hand, a magnetic design associated with a part that deforms under the effect of the exerted torque and, on the other, a Hall-effect sensor associated with a generally unconstrained part. Such devices are based on the use of a magnetic design that represents a quick transition opposite which is positioned the analog-output Hall-effect sensor.
Such devices have the following disadvantages: The sensitivity of the sensor may vary as a function of temperature. In fact, the latter takes into account the drift of the sensor and the magnets. Some correction principles consist of using a Hall-effect sensor that partially compensates for the drift in temperature of the magnets or appropriate electronic processing. This principle results in limited performance, once random drifts and sensor offsets are taken into account. Also, a magnetic shielding device must be used in order to overcome any outside magnetic disturbances. And, the sensor components must be positioned accurately, opposite the magnetic transition, in order to minimize magnetic offset, and the zero temperature drift that results from it.
There also are known devices capable of detecting the relative movement of a source of a magnetic field and comprising several Hall probes combined together in a subassembly and placed in a predetermined layout and possibly in a straight line.
Documents WO A 94 05 974 and WO A 94 05 975 describe devices comprising Hall-effect components positioned at a predetermined distance from one another in a predetermined layout. Document EP A 590 222 describes a magnetic position sensor capable of detecting the positions of a magnetic component having a field component that is canceled out in at least one point in space, the sensor including a network of Hall-effect probes aligned in a direction perpendicular to this field component and to the current circulating through the probes. We also refer you to document EP A 591 113. Document WO A 93 22 623 describes a device that generates a cumulative signal representing the position of a magnet in relation to a linear series of Halle-effect switches.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the invention, this is provided by a torque sensor to determine the torque exerted on an assembly comprising a component generating magnetic impulses. The sensor comprises a plurality of aligned sensor components that are divided into at least two subassemblies, the signals emitted by the subassemblies being processed by an electronic circuit capable of delivering an analog signal as a function of the torque exerted. The sensor components, even in number for example, are chosen from among the groups including Hall-effect probes, magnetic resistances, and giant magnetic resistances, and they are positioned equidistant from one another.
In another aspect of the invention, this is provided by a process for processing a signal emitted by a torque sensor having a plurality of aligned sensor components, the process comprising the following steps: creation of at least two subassemblies of N sensor components; adding signals emitted by each sensor component of the first subassembly to form first sum S1; adding signals emitted by each sensor component of the second subassembly to form second sum S2; and adding signals S1 and xe2x88x92S2 to obtain a signal as a function of torque exerted. The choice of the number of sensor components chosen to create the subassemblies of sensor components may be made using programs of EEPROM, ZENER ZAPPING type, or the like.
In a variant of the invention, a multiple of four sensor components is used to form four subassemblies for signal process too obtain a signal as a function of the torque exerted. In a subvariant, a programmable gain G is applied to signal COS and/or to signal SIN in order to obtain signal SIN+G.COS or G.SIN+COS as a function of the torque exerted which intensity is null when the exerted torque is null. The process may include the following steps: detecting a maximum signal emitted by each sensor component; and regulating the sensitivity of the sensor as a function of the maximum signal detected.
According to a third aspect, a device is proposed for implementing a process described above, including a customized ASIC type of integrated circuit. According to a fourth aspect, a torque sensor assembly as described above is combined with such a device, wherein the sensor components of the sensor are included in the customized ASIC integrated circuit. According to a fifth aspect, the above-described assembly is applied to determine torque by detecting relative movement of the sensor components with respect to at least two pairs of magnetic poles with inverted magnetic direction of a given pole in relation to those that are contiguous to it so as to reduce edge effects and to obtain a sinusoidal magnetic field over the entire measurement area.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.